Shannalee Sharbonneau wishes she’d never treated herself to that bracelet last June. It was featured in the Duty Free magazine on her almost 11-hour KLM flight from Amsterdam to Johannesburg, where she would start the safari in South Africa she’d been planning for an entire year with her husband. “I’d never bought anything on a plane, but we were in a good mood, celebrating our anniversary,” she says. It did seem strange to Sharbonneau that the flight attendant who sold the jewelry had popped the American Express card into her apron and disappeared for 20 minutes or more, but Shannalee shrugged it off. After arriving in Johannesburg, the couple was whisked off on their safari for ten days, free of cell phone service or Wi-Fi.

It was only when the couple went for lunch in a nearby town that Sharbonneau’s concerns proved prescient. On that same credit card, she found thousands of dollars in unauthorized charges: the same fraudsters had hacked into the online account associated with the card, transferring $5,000 from the linked bank account to offset those charges. Sharbonnea called Amex, which leapt into action; the fraud team at the credit card company told her this was a sophisticated con, probably a ring that used software to crack the encryption. The couple wasn’t held liable, since the fraud had begun when they were entirely offline in the bush—but immediately after the furtive behavior of that flight attendant.

We can't know if Sharbonneau’s experience is underreported—it’s not reported at all. There are no reliable statistics on in-flight theft of any kind, whether pickpocketing or credit card cloning. Spokespeople for the FAA, TSA, and AAAE (American Association of Airport Executives) all told Condé Nast Traveler they did not have access to, or had ever seen, such data. The DOT cited this report, which includes information on mishandled baggage without breaking down figures between loss, damage, delay, or theft.

If anything, it’s a reminder of how vulnerable, even trusting, we tend to be when flying. Travelers often won’t notice an item missing from a bag until they arrive home—when they can’t be sure when the theft occurred, or even if it was a crime. Those who do report in a timely fashion usually opt to complain to the airline rather than the police, since they’re focused mostly on swift compensation. A crime aboard an aircraft is a federally prosecutable offense, and once a plane crosses state lines, the charge of interstate transportation of stolen property also kicks in; unfortunately, the FBI doesn’t keep standalone records on in-air theft.

It’s an easy crime to get away with, because no one is paying attention.

“It’s an easy crime to get away with, because no one is paying attention,” says Jeff Price, a professor at Metropolitan State University of Denver and an airport management expert. “It’s impractical to run the entire passenger list to see who might have a record for theft, and the cost of what’s stolen—we’re not talking massive grand larceny, so [law enforcement] might not put much effort into it.” As for airlines, they’re understandably tight-lipped about the problem: They already have to self-report flight delays and mishandled baggage (including pets), and throw things that don’t fit into the all-encompassing “consumer complaints” category.

Though theft at 33,000 feet does happen, it’s exceedingly rare. One security executive from a legacy airline, now retired, said problems were flagged once or twice a year during his tenure, but the issue has escalated since. “It’s very much an ‘in’ subject at the moment with the airline industry,” says aviation security expert Philip Baum, who runs courses on safety and security in the sector. “Over the last two years, at the request of the airlines, we’ve developed modules [for airline staff] specifically about in-flight theft,” he says. These include everything from how the thieves operate to the kind of passengers and routes they’re likely to target, and the best way to liaise with law enforcement before suspects deplane.

Certainly, periodic news stories suggest in-flight theft occurs in brazen ways. Earlier this year, after Hong Kong-based journalist Yonden Lhatoo wrote about losing $3,000 in cash from his carry-on while it was stashed over his seat, a deluge of his readers shared their own stories. Lhatoo didn’t witness any suspicious behavior—unlike businesswoman Carol Baez, on a red-eye from Dallas to Paris four years ago. She woke, mid-flight, to see a male cabin crew member emerge from the bathroom carrying her rifled-through purse (it was investigated and he was fired). In 2010, one Air France staffer known as Lucie R confessed to 27 different counts of theft, including cash, jewelry, and credit cards, mostly while working on the Tokyo-Paris route.

Jack R. Plaxe, a veteran security expert with more than a decade of experience working within the airline industry, says organized rings are by far the biggest problem. A typical scenario involves a pair of crooks who will buy tickets for a red-eye in economy in peak season—it’s much easier to commit a crime there, since the cabin is larger, busier, and more anonymous.

“They sit in the gate area and observe passengers, profile them, to try to identify who may be good targets—what they’re placing into their bags, for example,” Plaxe says. Once the mark is identified in this way, the would-be thieves will board early and observe as bags are stowed; they might then casually move their own bag into the same locker as their target. One member of the pair will then commit the crime, either during the chaotic, stressful boarding process or once the cabin lights are dimmed for sleeping. As insurance against being spotted and then searched, the culprit will then pass any items on to an accomplice. “It’s very similar to what pickpockets do in public places: one person steals from you when you’re distracted, then hands it off to another person, who escapes,” says Plaxe. A few pairs might add the insurance of a third member, who can act as a lookout, or another mule who will also exit the plane with some of the bounty.

How, then, to ensure against becoming a victim on in-flight theft?

There are some simple safeguards. Be mindful at the gate area or in the airline lounge, another prime spot for crooks to case premium travelers. Don’t rummage through your bags and show off their contents. Always keep your valuables on your person or in a small bag at your feet, at all times, rather than in the overhead bin—that’s your passport, wallet, and any crucial medication. If you do place a rollaboard or other bag overhead, don’t put it directly above you: instead, put it across the aisle, slightly forward, so you can easily keep an eye on it. Turn it around so that the zipper or opening faces inwards, making discreet access harder.

Realize there are people on board that have the power to do some damage to you, and don’t let your instincts kick in later.

Note the route you’re flying, too. Almost every aviation security expert also says that in-flight theft is far more common in certain regions and areas. Per Baum, this includes regions where business is still transacted using large amounts of cash, making carry-ons especially rich pickings: He hears regular reports of incidents in Southeast Asia, Africa, and China, and on flights to and from Middle Eastern airports like Doha and Dubai.

Anthony Roman, a licensed commercial pilot who runs a U.S.-based risk management firm, agrees: “In regions of the world where carrying cash is the much preferred method of doing business—that’s the Middle East, some parts of Asia and Africa—passengers often travel with sums of cash that are quite large,” he says. “And can you demonstrate ownership of that large sum of cash? It’s cash, of course, so you can’t.” And Plaxe identifies flights to or from the major business hubs in those areas are particularly at risk, like Dubai or Hong Kong. And of course, follow your instincts: Don’t let anyone walk away with your credit card, for any reason.

More than anything, though, it’s vital to stay alert. Traveling in the air often strips away some of our innate self-awareness—an airplane is the classic non-place, a term coined by psychologist Marc Augé, for venues that seem transient and anonymous enough that the rules of everyday life don't apply. “Somehow, when people are being propelled through earth’s atmosphere at 33,000 feet they feel like they can get away with things they cannot do elsewhere,” says Baum. “They’re divorced from the laws of planet earth.” (See: the consistent theft of airlines’ upgraded bedding and pillows in the last couple of years by normally law-abiding folks.) Those noise-canceling headphones and eye masks don’t sharpen our senses, either.

There’s also a misleading sense of community in a cabin, says professor and security guru Jeff Price. “You feel like you’re in it together—after all, if something bad happens on a flight, it will affect everybody pretty equally,” he says. “You’ve all had to go through this traumatic experience that’s like an obstacle course where you feel like you’ve just finished military training: getting checked in, [going] through the screening checkpoint. There’s a sense of unity, that you’ll take care of each other. Whether that’s actually true or not, it doesn’t matter—people let their guards down quite a bit.”

This mindset certainly contributed to Sharbonneau’s problems, who tamped down her own misgivings at the flight attendant’s strange behavior. She’ll never buy anything on a flight again, of course, but wants other travelers to learn from her mistakes. “Realize there are people on board that have the power to do some damage to you, and don’t let your instincts kick in later.”